The president of Kenya declared victory over terrorists today saying that despite an "immense" loss of life during the attack on a Nairobi shopping mall, defense forces "ashamed and defeated our attackers."

President Uhuru Kenyatta described a scene of bloody carnage following a lengthy siege of the Westgate mall that left at least 72 people dead, including 61 civilians.

The death toll is expected to rise, he said, because in the final hours of fighting, three of the mall's floors collapsed, resulting in "several bodies still trapped in the rubble including the terrorists."

He said 240 people had been injured in the attack since armed members of al-Shabab, an Islamist terror organization linked to al-Qaeda, opened fire on shoppers on Saturday.

PHOTOS: Kenya Mall Attack

He described the terrorists as "craven wretches and lowly cowards."

The president said an investigation was ongoing to confirm the identities and nationalities of the victims and the attackers, and he said officials were trying to confirm reports that the attackers included a British woman and two or three Americans.

He declared three days of national mourning.

Just before Kenyatta broadcast his address, President Barack Obama spoke at the United Nations General Assembly, calling the terror attack a "tragedy."

The FBI is preparing to deploy a full team to Nairobi to investigate the attack, officials told ABC News. Agents are coming from a variety of places but the case is being led by the New York field office, which handles crimes against Americans that occur in Africa.

The FBI investigates crimes against Americans and U.S. interests overseas. The United States offered assistance to the Kenyan government soon after the assault began Saturday.

Kenyan authorities have claimed "full control" of the Westgate Mall as they sweep the shopping center for any remaining terrorists, hostages still in hiding and dead bodies.

"The West Gate Mall is under the full control of gov't forces and we are carrying out a sweep to ensure its safe for everyone," Kenyan police tweeted today on their official Twitter account.

Eleven soldiers were injured in the attack and are being treated for injuries, according to authorities.

The attack began Saturday when 12 to 15 al-Shabab militants wielding grenades and guns stormed the upscale mall and began firing on civilians. Eyewitnesses say the militants were shooting anyone who couldn't prove they were Muslim.

Arnold Mwaghacho, who was working at a gourmet burger bar when terrorists began their attack, was wounded in the attack and played dead so the militants would walk by his body.

"I took the blood that I was covered with. I rubbed it on my face so when they came there they think I'm dead," he said.

Among the dead are Australian architect Ross Langdon and his girlfriend, Elif Yavuz, a Harvard graduate who worked for The Clinton Foundation. Yavuz was eight months pregnant and was working with Bill Clinton's foundation to fight the spread of malaria and AIDS in Africa.

At least 18 foreigners were among the dead, including six Britons, as well as citizens from France, Canada, the Netherlands, Australia, Peru, India, Ghana, South Africa and China.

President Kenyatta's nephew and the man's fiancée were also killed in the siege.

Al-Shabab, which means "The Youth" in Arabic, said the mall attack was in retribution for Kenyan forces' 2011 push into neighboring Somalia. In response, the group has increasingly set its sights on soft targets like the Westgate Mall.